> On a related note, I can't make sense of the POSIX definitions from
> <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap03.html>:
>
> 3.391 System Clock
> A clock with at least one second resolution that contains seconds since
> the Epoch.
>
> 3.313 Real Time
> Time measured as total units elapsed by the system clock without regard
> to which thread is executing.
>
> 3.228 Monotonic Clock
> A clock measuring real time, whose value cannot be set via
> clock_settime() and which cannot have negative clock jumps.

"units elapsed by the system clock" -- does this mean "the value of the
system clock" or "how many times the system clock has advanced by one
unit of time since system startup"?